Use cases exist for fetching a single, discrete revision of a blueprint and also
generically fetching whatever the latest might be.

Use cases exist for fetching a single, discrete revision of a blueprint and also
generically fetching whatever the latest might be. In this way, we funnel all that
through a single function that either uses a different constraint to get a single
record, or in the latter case, sorts by descending revision and picks the head record.

Fetches the latest blueprint revision for every known blueprint. The idea here
is to provide insight into what blueprints exist in the system; given we have the
inspection API for checking specific revisions, simply showing what's available and
a pointer to the latest revision, should be informative enough.